我正在尝试将一些HBox添加到BorderPane的中心。当我按下按钮时，NullPointerException被打印出来。我不知道为什么，在教程应用程序中它工作。
在controllers.MainController.setCenter 在controllers.TopMenuButtonsController.todoOnAction
public class Main extends Application {
public static void main(String[] args) {
launch(args);
}
public void start(Stage primaryStage) throws Exception {
FXMLLoader fxmlLoader = new FXMLLoader(this.getClass().getResource("/fxml/BorderPaneMainFXML.fxml"));
BorderPane borderPane = fxmlLoader.load();
Scene scene = new Scene(borderPane);
primaryStage.setScene(scene);
primaryStage.setTitle("TITLE");
primaryStage.show();
}
}
public class TopMenuButtonsController {
@FXML
private MainController mainController;
public void setMainController(MainController mainController) {
this.mainController = mainController;
}
@FXML
public void todoOnAction() {
mainController.setCenter("/fxml/TodoFXML.fxml");
}
}
public class MainController {
@FXML
public BorderPane borderPane;
@FXML
public TopMenuButtonsController topMenuButtonsController;
@FXML
public void initialize(){
topMenuButtonsController.setMainController(this);
}
public void setCenter(String fxmlPatch) {
FXMLLoader fxmlLoader = new FXMLLoader(this.getClass().getResource(fxmlPatch));
Parent parent = null;
try {
parent = fxmlLoader.load();
} catch (IOException e) {
e.printStackTrace();
}
borderPane.setCenter(parent);
}
}
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.layout.VBox?>
<BorderPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="800.0" prefWidth="640.0" style="-fx-background-color: #2C3E50;" xmlns="http://javafx.com/javafx/8.0.111" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controllers.MainController" >
<top>
<VBox>
<fx:include fx:id="topMenuButtons" source="TopMenuButtons.fxml"/>
</VBox>
</top>
</BorderPane>
<?xml version="1.0" encoding="UTF-8"?>
<?import com.jfoenix.controls.JFXButton?>
<?import javafx.scene.layout.HBox?>
<?import javafx.scene.text.Font?>
<HBox maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" xmlns="http://javafx.com/javafx/8.0.111" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controllers.TopMenuButtonsController">
<children>
<JFXButton onAction="#todoOnAction" ripplerFill="#3498db" text="todo" textFill="#ecf0f1">
<font>
<Font name="MS Outlook" size="14.0" />
</font></JFXButton>
<JFXButton onAction="#gridOnAction" ripplerFill="#3497d9" text="grid" textFill="#ecf0f1">
<font>
<Font name="MS Outlook" size="14.0" />
</font></JFXButton>
<JFXButton onAction="#statsOnAction" ripplerFill="#3497d9" text="statistics" textFill="#ecf0f1">
<font>
<Font name="MS Outlook" size="14.0" />
</font></JFXButton>
<JFXButton onAction="#notesOnAction" ripplerFill="#3497d9" text="notes" textFill="#ecf0f1">
<font>
<Font name="MS Outlook" size="14.0" />
</font></JFXButton>
<JFXButton onAction="#prefOnActionn" ripplerFill="#3497d9" text="preferences" textFill="#ecf0f1">
<font>
<Font name="MS Outlook" size="14.0" />
</font></JFXButton>
<JFXButton onAction="#settingsOnAction" ripplerFill="#3497d9" text="settings" textFill="#ecf0f1">
<font>
<Font size="14.0" />
</font></JFXButton>
</children>
</HBox>
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.HBox?>
<HBox maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.111" xmlns:fx="http://javafx.com/fxml/1">
<children>
<Label prefHeight="136.0" prefWidth="221.0" text="Lasdfasdfsdafsdfsdbel" />
</children>
</HBox>
<!-- language: lang-none -->
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8413)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:381)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:417)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
... 48 more
Caused by: java.lang.NullPointerException
at controllers.MainController.setCenter(MainController.java:34)
at controllers.TopMenuButtonsController.todoOnAction(TopMenuButtonsController.java:40)
... 58 more
答案 0 :(得分：1)
您的<BorderPane>标记缺少fx:id属性，因此不会将其注入控制器。因此，borderPane在控制器中为空，并且在调用borderPane.setCenter(...)时会出现空指针异常。
你需要
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.layout.VBox?>
<BorderPane fx:id="borderPane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="800.0" prefWidth="640.0" style="-fx-background-color: #2C3E50;" xmlns="http://javafx.com/javafx/8.0.111" xmlns:fx="http://javafx.com/fxml/1" fx:controller="controllers.MainController" >
<top>
<VBox>
<fx:include fx:id="topMenuButtons" source="TopMenuButtons.fxml"/>
</VBox>
</top>
</BorderPane>